Study questions role of vitamin D in asthma

NEW YORK (Reuters Health) - Giving people with asthma and
low vitamin D levels extra doses of the vitamin doesn't do much
to help their lungs, a new study suggests.

Previous research had linked low vitamin D levels to more
asthma-related problems, like weaker lungs and more asthma
exacerbations.

But it wasn't clear if vitamin deficiencies were causing
those problems, or if giving patients extra vitamin D was the
answer.

Lead author Dr. Mario Castro from Washington University
School of Medicine in St. Louis, Missouri, said as many as
two-thirds of his asthma patients are lacking in vitamin D.

"Our thought was that vitamin D would potentially make . . .
the standard therapy, inhaled corticosteroids, work better in
these patients, and that it would reduce their asthma
exacerbations," he told Reuters Health.

To test that theory, the researchers studied just over 400
adults with asthma and low vitamin D levels. They randomly
assigned half of the participants to take vitamin D3 supplements
every day, and the other half to take a vitamin-free placebo
pill.

All of the patients also took corticosteroids to help keep
their asthma in check.

Over the next six months, Castro and his team tracked
so-called treatment failures - the times patients were sent to
the emergency room or hospitalized for asthma, had declines in
lung function or had to increase their use of asthma medication.

They found between one-quarter and one-third of participants
in both the vitamin D and placebo groups had a treatment failure
during the study. The only benefit linked to vitamin D was that
patients in the vitamin group needed slightly lower doses of
corticosteroids to control their asthma.

When the researchers looked only at patients whose vitamin D
levels significantly improved from the supplements, they found
benefits in some areas compared to the placebo group - such as
fewer patients with an asthma exacerbation - but not in other
areas.

The findings don't support using vitamin D as a general
treatment strategy for people struggling with asthma symptoms,
the authors write in the Journal of the American Medical
Association. They also presented their results Sunday at the
American Thoracic Society International Conference in San Diego.

Castro said he thinks it is still appropriate to treat some
asthma patients with vitamin D while more research is being
conducted. He prescribes it to people with low vitamin D levels
who also have uncontrolled asthma symptoms, and monitors them to
make sure their levels come up.

"I think there may be some benefit, and vitamin D is
inexpensive and has (minimal) side effects," he said.

Vitamin D3 supplements cost a few dollars per month for the
dose used for most of the study, about 4,000 international
units.

Dr. Ken Kunisaki from the University of Minnesota in
Minneapolis said there are still some questions, such as what is
a big enough dose of vitamin D to give people who are deficient.

But he said that in general, the new findings were
"disappointing."

Regarding the role of vitamin D in asthma, "It's been a
fairly consistent story from the observational studies,"
Kunisaki, who specializes in pulmonary and critical care
medicine, told Reuters Health.

Those studies relied on measuring people's vitamin D levels
and asthma symptoms, rather than instructing some patients to
take extra vitamin D. In observational studies, it's possible
another underlying factor could explain the link between low
vitamin D and asthma-related problems, he said.

"It goes to show why we do randomized clinical trials," said
Kunisaki, who wasn't involved in the new research.

"This study would say that at least in this population,
there's no role for routinely looking at vitamin D levels, at
least for asthma-control purposes," he concluded.

The study was funded by the National Institutes of Health,
and the asthma medications used were provided free of charge by
their manufacturer, Sunovion Pharmaceuticals.

SOURCE: http://bit.ly/Tm0zFL Journal of the American Medical
Association, online May 18, 2014.